Mixed wire semiconductor lead frame package

ABSTRACT

One embodiment includes an encapsulated semiconductor package having a lead frame with die pad surrounded by a plurality of first and second leadfingers. A semiconductor chip including chip contact pads on its upper active surface is attached to the die pad. A plurality of first bond wires, incoluding a first electrically conductive material, extend between the chip contact pads and the plurality of first leadfingers. A plurality of second bond wires, including a second electrically conductive material, extend between a chip contact pad and a second leadfinger. The semiconductor package further includes a plurality of electrically conducting means attached to the second leadfingers.

CROSS REFERENCE TO RELATED APPLICATION

This Utility Patent Application is a divisional application of U.S.application Ser. No. 11/660,854, filed Jun. 4, 2008, and claims thebenefit of the filing date of International Application No.PCT/IB2004/002696, filed Aug. 19, 2004, which are both incorporatedherein by reference.

BACKGROUND

One aspect of the invention relates to an improved mixed wiresemiconductor lead frame package and a method for producing the package.

Mixed wire semiconductor lead frame packages which include twopluralities of bond wires, each including a different metal, are known.A package 1 of the prior art is illustrated in FIG. 1. The package 1includes a copper lead frame 2 with a recessed die pad 3 laterallysurrounded by a plurality of leadfingers 4 and a semiconductor chip 5which is mounted to the die pad 3 with die attach material 6. Thesemiconductor chip 5 includes integrated circuit devices 7 on its upperactive surface and a plurality of chip contact pads 8. Some devices areelectrically connected to the lead frame 2 by aluminium bond wires 9 andother devices by gold bond wires 10.

Aluminium bond wires 9 of a large diameter are commonly used toelectrically connect power devices to the lead frame 2 since a highcurrent capacity is desired. A wedge-bonding technique is commonly usedfor the aluminium bond wires 9 and a large laterally rectangular bondpad is provided on the chip 5 which increases the chip dimensions. Thechip contact pads of devices which require a smaller current capacityare connected to the lead frame by gold wires 10 which typically have asmaller diameter than the aluminium bond wires 9. The gold wires 10 arebonded using a ball bonding technique. Smaller laterally square contactpads are provided on the semiconductor chip 5 for the gold ball bonds.

The aluminium bond wires 9 and gold bond wires 10 are bonded to landingpads 11, 12, respectively, provided on the inner portion of theleadfingers 4. Since a silver-aluminium interface is known to beunreliable, landing pads 11, 12 including two different materials areprovided. The landing pads 11 include NiNiP for the aluminium bond wires9, whereas the landing pads 12 for the gold bond wires 10 includesilver, in order that the bond wires 9, 10 form a bond and, therefore, agood electrical connection with the landing pads 11, 12 respectively.

Therefore, in order to manufacture the lead frame 2, which is suitablefor the mixed wire semiconductor package 1, the lead frame 2 undergoestwo precision electro-plating process steps; one in which the NiNiPlanding pads 11 are electroplated and one in which the silver landingpads 12 are electroplated.

The requirement of two precision electroplating process steps leads tohigh production costs for mixed wire semiconductor packages and thepotential risk of cross contamination of the lead frame during theeletroplating of the different metals.

SUMMARY

One embodiment of the invention provides an improved mixed wiresemiconductor package and a simplified manufacturing process in whichthe disadvantages associated with multiple precision electroplatingprocess steps are avoided.

One embodiment of the invention provides an improved mixed wiremulti-chip semiconductor package.

A semiconductor package according to one embodiment of the inventionincludes a lead frame with a die pad, a plurality of first leadfingersand a plurality of second leadfingers. Each of the first and secondleadfingers includes a landing pad positioned on its inner portiontowards the inner end of the leadfinger.

One embodiment of the semiconductor package also includes asemiconductor chip including a plurality of integrated circuit devicesand a plurality of chip contact pads on its upper active surface. Thesemiconductor chip is attached to the die pad by its rear passivesurface by conventional die attach material, as is well known in theart.

One embodiment of the semiconductor package further includes a pluralityof first bond wires including a first electrically conductive material.Each first bond wire extends between a chip contact pad and a landingpad positioned on the plurality of first leadfingers.

A plurality of second bond wires, which includes a second electricallyconductive material, is also provided in the semiconductor packageaccording to one embodiment of the invention. Each second bond wireextends between a chip contact pad and a second leadfinger.

In one embodiment, a plastic mould mass encapsulates the semiconductorchip, the pluralities of first and second bond wires and inner portionsof the pluralities of first leadfingers and second leadfingers to forman encapsulated mixed wire semiconductor lead frame package.

The semiconductor package according to one embodiment of the inventionincludes a plurality of first electrically conducting means. A firstelectrically conducting means is attached to the landing pad of each ofthe plurality of second leadfingers and a second bond wire extendsbetween, and is attached to, a chip contact pad and a first electricallyconducting means.

One embodiment of the invention further provides a semiconductor packagewhich includes at least two semiconductor chips. Such packages arecommonly referred to as multi-chip semiconductor packages or multi-chipmodules. The multi-chip module according to one embodiment of theinvention includes a lead frame having at least a die pad, a pluralityof first leadfingers and a plurality of second leadfingers, eachincluding a landing pad on its inner portion.

The multi-chip module further includes at least two semiconductor chipsincluding integrated circuits and chip contact pads on their upperactive surfaces. The semiconductor chips are attached to the die pad bytheir rear passive surfaces.

A plurality of first bond wires including a first electricallyconductive material is provided, each extending between a chip contactpad and a landing pad of the plurality of first leadfingers. A pluralityof second bond wires including a second electrically conductive materialis provided, each extending between a chip contact pad and a secondleadfinger. A plurality of third bond wires including a thirdelectrically conductive material extending between the semiconductorchips.

A plastic mould mass encapsulates the semiconductor chips, thepluralities of first, second and third bond wires and inner portions ofthe pluralities of first leadfingers and second leadfingers.

The multi-chip module further includes a plurality of first electricallyconducting means. A first electrically conducting means is attached tothe landing pad of each of the plurality of second leadfingers, and asecond bond wire is attached to the first electrically conducting means.

In contrast to the mixed wire packages known in the art, the mixed wiresemiconductor packages according to the invention, therefore, includelanding pads, which inlcude essentially the same material and which aredeposited in the same step of the manufacturing process, on both thepluralities of first and second leadfingers. Therefore, multipleprecision or selective electro-plating or electro-deposition steps areavoided.

The semiconductor packages of the invention, for example, includes alead frame with a recessed die pad and, in one example, at least one diepad lead.

In one example, the plurality of first electrically conductive meansincludes a plurality of electrically conductive bumps or electricallyconductive wedges or electrically conductive balls. The firstelectrically conductive means are formed using a ball-bonding or awedge-bonding technique. Since these techniques are used for formingbond connections between the chip and lead frame in the package, theadditional complexity and cost of providing new equipment is, therefore,avoided.

The plurality of first electrically conducting means in one example, hasan approximately rectangular longitudinal cross-section and ispositioned on the landing pad of the second leadfinger with its longside of approximately parallel to the length of the second leadfinger orapproximately orthogonal to the length of the second leadfinger. In oneexample, a first electrical conducting means positioned approximatelyorthogonal to the length of the second leadfinger is advantageous if twoor more wires are to be bonded to a landing pad of a second leadfinger.Alternatively, the first electrically conductive means can have anylateral orientation with respect to the length of the second leadfinger.

In one example, the plurality of first bond wires is attached to thelanding pads of the first leadfingers with a ball-bond, bump or awedge-bond and the plurality of second bond wires is attached to thefirst electrically conducting means on the second leadfingers with aball-bond, a bump, a wedge-bond or a stitch-bond.

The reliability of the bond connection is improved if the interfacialarea between the bond wire and the first electrically conductive meansis increased. If, for example, the first electrically conductive meanshas an approximately rectangular longitudinal cross-section, forexample, it is a wedge, its lateral orientation on the landing pad ofthe second leadfinger is chosen to increase the interfacial area bylaterally orientating the conductive means and bond wire inapproximately the same orientation. Alternatively, if the second bondwire is attached by a wedge-bond to the electrically conductive meanswhich itself has an approximately rectangular longitudinally orientatedwedge form, then a bond between the wire and first electricallyconductive means can be more reliably formed, as the relativepositioning is more flexible, if they are mutually approximatelyorthogonally orientated.

However, if, for example, the second bond wire is bonded to the firstelectrically conductive means using a ball-bond and therefore has asymmetrical and approximately circular lateral bond surface and thefirst electrically conductive means has an approximately rectangularlongitudinal cross-section, then the interfacial area between the bondwire and first electrically conductive means is essentially the same forall lateral orientations of the first electrically conductive means.Therefore, the first electrically conductive means can be orientated onthe landing pad so as to the advantage of the manufacturing process, forexample by minimising the movement of the bonding tool.

The first electrically conductive means may have a variety oforientations or forms on a lead frame of a single package. This enablesan increased flexibility for the bonding process.

In one example, the plurality of second bond wires and plurality ofelectrically conducting means include a different material. Theplurality of first bond wires and the plurality of electricallyconducting means in one example include essentially the same material.This enables the first bond wires and first electrically conductivemeans to be formed in the same manufacturing process step, thussimplifying the manufacturing process and saving time and costs.

In one example, under typical wire-bonding conditions, the material ofthe first bond wire and the material of the landing pad form a eutectic,the material of the electrically conducting means and the material ofthe landing pad form a eutectic, the material of the second bond wireand the material of the landing pad form no eutectic, and the materialof the second bond wire and the material of the electrically conductingmeans form a eutectic. Typical conditions used to form a bond betweenthe bond wires and the landing pads which include various materials in,for example, ball-bonding, wedge-bonding and stitch-bonding techniquesare known in the art.

The formation of a eutectic between two metals or metal alloys is wellknown. Under certain conditions, for example temperature and pressure, aeutectic mixture of the two metals is formed. The eutectic mixture has alower melting point than that of each of the pure metals. This effect isused in the bonding process to form a melt at the interface between thebond wire and landing pad providing a good electrical and mechanicalbond between the wire and landing pad without melting the body of thebond wire or landing pad.

Since the material of the second bond wire and the material of thelanding pad form no eutectic under typical wire bonding conditions, agood electrical and mechanical bond is not formed. Therefore, a firstelectrically conductive means including a material which forms aeutectic with the material of the landing pad and a eutectic with thematerial of the second bond wire is placed between the second bond wireand the landing pad. A good electrical and mechanical bond is,therefore, formed between the first electrically conductive means andthe landing pad and between the second bond wire and the firstelectrically conductive means. Since the material of the first bond wireand the material of the landing pad form a eutectic a good electricaland mechanical bond is formed and a first electrically conductive meansis not included.

The first electrically conductive means has the function of anintermediate or a buffer material which enables the landing pads of thefirst and second leadfingers to include essentially the same material.The landing pads for both the first and second bond wires are depositedin a single electroplating step in the production process, thusproviding a simpler process and saving time and costs.

Since the first electrically conductive means in one example include aball-bond or a wedge bond, they are formed in the same stage of theprocess as the bond wire connections. If the first electricallyconductive means and the first bond wire means include essentially thesame material and the same type of bond, for example a wedge bond, thenthey can be formed in the same manufacturing process step. This avoids athird bonding tool and a third material as well as saving productiontime, material. Production costs and, ultimately, the cost of thesemiconductor package are reduced.

In one example, the lead frame includes copper or a copper alloy, thelanding pads include a layer of nickel positioned on the surface of thefirst and second leadfingers and a layer of nickel phosphorouspositioned on the layer of nickel, the plurality of first bond wires andthe electrically conducting means include aluminium or an aluminiumalloy and the plurality of second bond wires include gold or a goldalloy.

In this case, the aluminium or aluminium alloy of the first bond wiresand first electrically conductive means forms a eutectic with the NiNiPlanding pad under typical bonding conditions and the gold or gold alloyof the second bond wires forms a eutectic with the aluminium conductivemeans. Gold and gold alloys form no eutectic with NiNiP under typicalbonding conditions.

The lead frame includes copper or a copper alloy, the landing padsinclude a silver layer positioned on the surface of the first and secondleadfingers, the plurality of first bond wires and the electricallyconducting means include gold or a gold alloy and the plurality ofsecond bond wires include aluminium or an aluminium alloy.

A lead frame of copper or a copper alloy has the advantage that theproduction methods are well-known, the material is available in highpurity and is relatively inexpensive. Ni, NiNiP and silver landing padsare also well-known and selective electro-deposition techniques arereliable.

The semiconductor package including one or at least two semiconductorchips in one example, includes at least one second electricallyconducting means attached to at least one chip contact pad. The secondelectrically conductive means, in one example, includes electricallyconductive bumps, electrically conductive wedges or electricallyconductive balls. The second electrically conductive means is, in oneexample, positioned between, and electrically connected to, the chipcontact pad and a bond wire.

The second electrically conducting means has an approximatelyrectangular longitudinal cross-section and is positioned on the chip padwith its long side of approximately parallel to the length of the chippad. Alternatively, the second electrically conducting means has anapproximately rectangular longitudinal cross-section and is positionedon the chip pad with its long side of approximately orthogonal to thelength of the chip pad. Alternatively, the second electricallyconductive means is orientated on the chip pad with any lateralorientation. This has the advantage that the interfacial area betweenthe bond wire and the second electrically conductive means can beincreased.

In one example, the second electrically conductive means includesessentially the same material as the first conductive means. This allowsthe first and second conductive means to be formed in the same step ofthe manufacturing process and reduces manufacturing time and costs.

The semiconductor package according to the invention, in one example,further includes a plurality of grounding pads positioned on the diepad. This enables the chip to be grounded to the lead frame of thesemiconductor package. A plurality of grounding electrically conductingmeans is, in one example, positioned on the grounding pads and agrounding wire extending between a chip contact pad and the groundingelectrically conductive means electrically connects the chip with thelead frame.

The provision of the grounding electrically conductive means on thegrounding pad enables the grounding pad to include essentially the samematerial as that of the landing pads so that both the landing pads andgrounding pads can be deposited at the same time. This avoids furtherelectro-plating steps, simplifying the fabrication of the semiconductorpackage and reducing costs.

The plurality of grounding electrically conductive means, in oneexample, includes a plurality of electrically conductive bumps orelectrically conductive wedges or electrically conductive balls. Thisenables the grounding electrically conductive means to be formed duringthe same stage of the manufacturing process as the first electricallyconductive means which are positioned on the landing pads.

The plurality of grounding bond wires is attached to the groundingelectrically conducting means on the die pad with a ball-bond, a bump ora stitch bond, the most appropriate bond type is provided so that, forexample, the bond type is compatible with the material of the wire.

In one example, under wire-bonding conditions the material of the firstbond wire and the material of the landing pad form a eutectic, thematerial of the first electrically conducting means forms a eutecticwith the material of the landing pad, the material of the second bondwire and the material of the landing pad form no eutectic, the materialof the second bond wire and the material of the first electricallyconducting means form a eutectic, the material of the groundingelectrically conductive means and the material of the grounding pad forma eutectic, and the material of the grounding wire and the material ofthe grounding electrically conductive means form a eutectic.

Therefore, a good and reliable bond is formed between the first bondwire and the landing pad, the second bond wire and the firstelectrically conductive means and the first electrically conductivemeans the landing pad. A good bond is also formed between the groundingwire and the grounding electrically conductive means and the groundingelectrically conductive means and the grounding pad. A reliablegrounding of the chip to the lead frame is, therefore, provided.

The lead frame, in one example, includes copper, and similarly to thelanding pads, the grounding pads include a layer of nickel positioned onthe surface of the die pad of the lead frame and a layer of nickelphosphorous positioned on the layer of nickel. In one example, theplurality of first bond wires, the electrically conducting means and thegrounding electrically conductive means include aluminium or analuminium alloy and the plurality of second bond wires and the pluralityof grounding wires include gold or a gold alloy.

This allows the grounding pads to be formed in the same electro-platingsteps as the landing pads and therefore further processing steps are notintroduced into the manufacturing line reducing the production costs.Also, since the grounding and first electrically conductive meansinclude essentially the same material, the first and groundingelectrically conductive means may be fabricated in the same processstep. Since the second and grounding bond wires include the samematerial, the second and grounding bond wires can be provided in thesame process step.

The manufacture of the package is, therefore, simplified and costsreduced as the number of different materials used in the package is notincreased.

In the multi-chip module according to the invention, the plurality ofthird bond wires, in one example, include essentially the same materialas the plurality of second bond wires or the plurality of first bondwires. The plurality of third bond wires is, in one example, attached tothe chip pads of the first and second semiconductor chips with a ballbond, a bump or a wedge bond. Alternatively, the plurality of third bondwires is attached to the second electrically conductive means positionedon the chip pads with a ball bond, a bump or a wedge bond.

A first semiconductor chip of the multi-chip module is, in one exampleelectrically connected by first bond wires to the plurality of firstleadfingers. A second semiconductor chip is, in one example,electrically connected by second bond wires to the plurality of secondleadfingers. This arrangement is advantageous as the most appropriatetype of bond wire can be chosen for the integrated circuits of each typeof semiconductor chip.

The multi-chip module, in one example, includes at least one logicsemiconductor chip and at least one power semiconductor chip. More inone example, the multi-chip module includes at least one power chipelectrically connected to the first leadfingers of the lead frame by aplurality of first bond wires and at least one logic chip electricallyconnected to the first electrical means of the second leadfingers of thelead frame by a plurality of second bond wires.

In one example, in the multi-chip module according to one embodiment ofthe invention, the first bond wires include aluminium or an aluminiumalloy, the second bond wires include gold or a gold alloy, the firstelectrical means includes aluminium, the lead frame includes copper andthe landing pads include Ni and NiP.

The bond wires connecting the logic chip to the second leadfingers,which in one case include first electrically conductive means, forexample, include gold. The bond wires connecting the power chip to thefirst leadfingers of the lead frame and to the logic chip in one exampleinclude aluminium and, in one example, have a larger diameter than thegold bond wires. The larger diameter is advantageous for the supply ofhigh currents.

The chip pads, in one example, have a rectangular form for the bondwires connected using a wedge bond and a square form for bond wiresconnected using a ball bond. A rectangular chip pad is advantageous forwedge bonds as the interface formed between the chip pad and the wedgebond is of a rectangular form.

One embodiment of the invention also provides methods to assemblesemiconductor packages. One method includes the following steps.

Firstly, a lead frame including a die pad, a plurality of firstleadfingers and a plurality of second leadfingers is provided. The leadframe is produced by etching or stamping methods known in the art.Initially, a lead frame strip including a plurality of lead frames isformed in which the plurality of lead frames are orientated in rows andcolumns forming an array. The individual lead frames are connected tothe lead frame strip surround and to each other by tie bars which areremoved at a later stage of the process to form individual lead framepackages.

A landing pad is then deposited on the inner portion of each firstleadfinger and each second leadfinger. A semiconductor chip including aplurality of integrated circuit devices and a plurality of chip contactpads on its upper active surface is provided. The passive rear surfaceof the semiconductor chip is attached to the die pad using conventionaldie attach material.

A first electrically conducting means is then formed on each landing padof the plurality of second leadfingers.

Bond connections are formed between the chip contact pads and landingpads of the plurality of first leadfingers with first bond wires. Bondconnections are formed between the chip contact pads and firstelectrically conducting means of the plurality of second leadfingerswith second bond wires.

The semiconductor chip, the first and second bond wires and inner endsof the pluralities of first and second leadfingers are then encapsulatedin a plastic mould material.

A method according to one embodiment of the invention to assemble asemiconductor package including at least two semiconductor chipsincludes the following steps. A lead frame including a die pad, aplurality of first leadfingers and a plurality of second leadfingers isprovided. A plurality of landing pads is deposited on the inner portionof the first leadfinger and second leadfingers and at least twosemiconductor chips including integrated circuits and chip contact padson the upper active surface are attached by the passive rear surface tothe die pad.

A plurality of first electrically conducting means is formed on thelanding pads of each of the plurality of second leadfingers.

First bond connections are then formed between the chip contact pads andlanding pads of the plurality of first leadfingers with first bondwires. Second bond connections are formed between the chip contact padsand electrically conducting means of the plurality of second leadfingerswith second bond wires. Third bond connections are formed between thesemiconductor chips with third bond wires.

The semiconductor chips, the pluralities of first second and third bondwires and inner ends of leadfingers are encapsulated in a plastic mouldmaterial.

In one example, the lead frame includes a recessed die pad and at leastone die pad lead. A recessed die pad is typically formed by a pressingtechnique.

In one example, the first electrically conducting means has anapproximately rectangular longitudinal cross-section and is formed onthe landing pad of the second leadfinger approximately parallel to thelength of the second leadfinger or approximately orthogonal to thelength of the second leadfinger. Alternatively, the first electricallyconductive means laterally positioned with any lateral orientation withrespect to the length of the second lead finger.

In one example, the first electrically conducting means is formed by awedge-bonding technique or a ball bonding technique. These techniquesare reliable well known and widely used. Therefore, start-up costs canbe saved as the existing production line can be used.

In one example, the landing pads are formed by depositing a first layeron the surface of the leadfinger and by depositing a second layer on thefirst layer. This has the advantage of forming a reliable landing padwhich forms a good bond with the material of the lead frame and with thefirst bond wire and electrically conductive means. In one example, thelanding pads are deposited using a selective electro-deposition orelectro-plating technique. Selective electro-plating techniques arewell-known in the art.

Since the landing pads of both the first and second leadfingers areelectro-plated at essentially the same time in a single process step,the manufacturing process is simplified and costs are saved. A furtheradvantage of the method according to one embodiment of the invention isthat since a conventional lead frame, i.e. all the landing pads includeessentially the same material, is used, the same lead frame can be usedfor different semiconductor products and the flexibility of havingvarious products in the internal configuration of the same packagewithout changing the lead frame type is enabled.

In one example, the plurality of first bond wires is attached to thechip contact pads and the landing pads of the plurality of firstleadfingers using a ball-bonding or a wedge-bonding technique and theplurality of second bond wires are attached to the chip contact pads andthe first electrically conducting means of the plurality of secondleadfingers using a ball-bonding or a wedge-bonding or a stitch-bondingtechnique. These techniques are well-known and reliable.

If the first bond wires and electrically conductive means includeessentially the same material and are formed using the same technique,for example a wedge bonding technique, then they can be formed in thesame process step. All of the electrically conductive means can beformed on the landing pads of the second leadfingers in a first stagefollowed by forming all of the bond connections between the chip contactpad and the landing pad of the first leadfingers by first bond wires orthese steps can be reversed. Alternatively, the electrically conductivemeans and the first wire bonds can be made in a mixed way in the sameprocess step. This has the advantage that the movement of the tool canbe minimised and collisions between formed bonds and the movement of thetool can be avoided.

In one example, the lead frame includes copper or a copper alloy, thelanding pads include a layer of nickel positioned on the surface of thefirst and second leadfingers and a layer of nickel phosphorouspositioned on the layer of nickel, the plurality of first bond wires andthe electrically conducting means include aluminium or an aluminiumalloy and the plurality of second bond wires include gold or a goldalloy.

The gold wires are bonded by a ball bonding technique which usestemperature and pressure to form the bond and the aluminium wires are,more in one example, bonded using a wedge bonding technique which usesmainly ultrasonic energy and force to form the bond. Gold ball bondingis, in one example, used for bonding over active circuits and chips withdelicate, such as low thermal expansion material, layers.

At least one second electrically conducting means is, in one example,attached to at least one chip contact pad. The plurality of secondelectrically conductive means is, in one example, formed by aball-bonding or a wedge-bonding technique.

The second electrically conducting means has an approximatelyrectangular longitudinal cross-section and is formed on the chip padwith its long side of approximately parallel to the length of the chippad. Alternatively, the second electrically conducting means has anapproximately rectangular longitudinal cross-section and is positionedon the chip pad with its long side of approximately orthogonal to thelength of the chip pad. The lateral orientation of the secondelectrically conducting means is, in one example, chosen so as toincrease the interfacial area between the bond wire and the secondelectrically conductive means.

The second electrically conductive means is, in one example,electrically connected to the chip contact pad and a bond wire.

The method to assemble the package according to the invention furtherincludes the steps of depositing at least one grounding pad on the diepad. A grounding electrically conductive means is then formed on thegrounding pad and bond connections are formed between contact pads onthe chip and the grounding electrically conductive means. This enablesthe chip to be grounded to the lead frame.

In one example, the grounding pads are formed by depositing a firstlayer on the surface of the die pad and by depositing a second layer onthe first layer. The grounding pads are, in one example, deposited usinga selective electro-deposition technique which is well-known in the artand inexpensive. More in one example, the grounding pads are formed inthe same process steps as the landing pads. This further reduces thecosts and complexity of the assembly process as only one masking stepfor the electro-plating process is required.

The plurality of grounding bond wires are, in one example, attached tothe chip contact pads and the grounding electrically conductive meansusing a ball-bonding or a wedge-bonding or a stitch-bonding technique.These techniques are well known in the art and the most appropriatetechnique depends on a number of factors known in the art such as thematerial of the bond wire. The grounding wire is attached to the chippad with a ball-bond and to the grounding electrically conductive meanswith a stitch-bond.

In the multi-chip module according to one embodiment of the invention,in one example, at least one power semiconductor chip and at least onelogic semiconductor chip are attached to the die pad.

In one example, at least one power chip is electrically connected to thefirst leadfingers of the lead frame by a plurality of first bond wiresand at least one logic chip is electrically connected to the firstelectrical means of the second leadfingers of the lead frame by aplurality of second bond wires.

The plurality of third bond wires is attached to the chip pads of the atleast two semiconductor chips by a ball-bonding or a wedge-bonding or astitch-bonding technique. Alternatively, the plurality of third bondwires is attached to the second electrically conductive means positionedon the chip pads by a ball-bonding or a wedge-bonding or astitch-bonding technique, and in one example, by a stitch bond.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates an encapsulated mixed wire semiconductor lead framepackage known in the prior art.

FIG. 2 illustrates an encapsulated mixed wire semiconductor packageaccording to a first embodiment of the invention.

FIG. 3 illustrates an encapsulated mixed wire semiconductor packageaccording to a second embodiment of the invention.

FIG. 4 illustrates an encapsulated mixed wire semiconductor packageaccording to a third embodiment of the invention.

FIG. 5 illustrates a schematic diagram of the first step in theformation of a wedge according to the invention.

FIG. 6 illustrates a schematic diagram of the second step of in theformation of a wedge according to the invention.

FIG. 7 illustrates an encapsulated mixed wire semiconductor packageaccording to a fourth embodiment of the invention.

FIG. 8 illustrates a first multi-chip module according to one embodimentof the invention.

FIG. 9 illustrates a second multi-chip module according to oneembodiment of the invention.

FIG. 10 illustrates a schematic perspective view of a section of a mixedwire semiconductor package including grounding connections according toone embodiment of the invention.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which isillustrated by way of illustration specific embodiments in which theinvention may be practiced. In this regard, directional terminology,such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc.,is used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments of the present inventioncan be positioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims.

FIG. 2 illustrates an encapsulated mixed wire semiconductor lead framepackage 20 which includes a semiconductor chip 21 attached to a recesseddie pad 22. The semiconductor chip 21 is electrically connected to aplurality of lead fingers 23, 24 of the lead frame 25 by a firstplurality of aluminium bond wires 26 and a second plurality of gold bondwires 27. The diameter of the aluminium bond wires 26 is larger thanthat of the gold bond wires 27.

The copper lead frame 25 includes a central recessed die pad 22laterally surrounded by two pluralities of lead fingers 23, 24. The diepad 22 is positioned lower in the package 20 than the lead fingers 23,24 so that the upper surface of the die pad 22 is positioned slightlylower than the bottom surface of the lead fingers 23, 24 with respect tothe top surface of the semiconductor package 20.

The lead frame 25 also includes two die pad leads 28 which extend fromthe die pad 22 to the outside of the encapsulated package 20. The diepad leads 28 enable the rear surface of the semiconductor chip 21 to begrounded at the same potential as that of the lead frame 25. There areno bond connections between the chip 21 and the die pad leads 28.

The inner portion of each of the lead fingers 23, 24 is located insidethe plastic encapsulation 39 of the package 20. Each lead finger 23, 24includes a landing pad 29 positioned on its upper surface towards theinner end of the inner portion. Each landing pad 29 includes two layers30, 31 which were deposited by an electroplating technique. Each landingpad 29 includes a layer of nickel 30 located on the surface of thecopper lead finger 23, 24 and a layer of nickel phosphorous 31positioned on the nickel layer 30.

The lead frame 25 according to the invention includes two pluralities oflead fingers 23, 24. They are distinguished in that the second pluralityof lead fingers 24 further include an aluminium wedge 32 which islocated on the upper surface of the landing pad 29. The first pluralityof lead fingers 23 include only a landing pad 29. The aluminium wedge 32is laterally orientated on the landing pad 29 so that its length liesapproximately parallel to the length of the second lead finger 24. Inthis cross-sectional view, the aluminium wedge 32 has an approximatelyrectangular cross-section in which the long side is horizontal. The twoend portions of the wedge 32 are raised slightly above the surface ofthe landing pad 29 so that only the central portion of the length of thewedge 32 is in contact with the landing pad 29.

The semiconductor chip 21 includes a plurality of chip contact pads 33on its upper surface and two pluralities of integrated circuits 34, 35.The back side of the chip 21 is attached by die attach material 36 tothe die pad 22 of the lead frame 25. The chip 21 is electricallyconnected by the first plurality of aluminium bond wires 26 connectedbetween the chip contact pads 33 of the first plurality of integratedcircuit devices 34 and the landing pads 29 of the first lead fingers 23.The second plurality of integrated circuit devices 35 are electricallyconnected by a second plurality of gold bond wires 27 to the aluminiumwedges 32 which are located on the landing pads 29 of the second leadfingers 24.

The aluminium bond wires 26 are bonded to the chip contact pads 33 andlanding pads 29 of the first lead fingers 23 by wedge-bonds 37 formedusing a wedge-bonding technique. Therefore, the end portions of thealuminium wire bonds 26 are positioned approximately parallel to theupper surface of the chip contact pad 33 and landing pad 29respectively.

The gold wires 27 are bonded to the chip contact pads 33 and thealuminium wedge 32 located on the second lead fingers 24 using a ballbonding technique. A gold bump 48 is formed on the surface of thealuminium wedge 32. A gold wire ball bond 38 is then formed at the chipcontact pad 33 and the gold wire 27 extends between the chip contact pad33 and the gold bump 48 positioned on the aluminium wedge 32 andelectrically connects the chip pad 33 with the second lead finger 24.The ball bond 38 formed at the end portion of the gold wire bond 27where the wire joins the surface of the chip contact pad 33 has anapproximately circular or oval cross-section.

The two pluralities of bond wires 26, 27, semiconductor chip 21, die pad22 and inner portions of the two pluralities of lead fingers 23, 24 areencapsulated by a plastic mould material 39 to form the mixed wiresemiconductor lead frame package 20 of the invention. The outer portionsof the lead fingers protruding from the plastic encapsulation 39 formthe outer contacts of the package 20. The outer contacts enable thepackage 20 to be mounted on an external substrate such as a printedcircuit board which is not illustrated in the diagram.

FIG. 3 illustrates a second embodiment of a mixed wire semiconductorlead frame package 40 according to the invention. Parts of the package40 which are essentially the same as those of the first embodiment 20illustrated in FIG. 2 have the same reference number and are notnecessarily described again.

In this embodiment of the invention, the aluminium wedge 41 is attachedto the landing pad 29 of the second lead finger 24 approximatelyorthogonally with respect to the length of the lead finger 24.Therefore, in the cross-sectional diagram illustrated in FIG. 3 thewedge 41 has an approximately oval cross-section.

In the second embodiment of the invention, the gold wire 27 is bonded tothe chip contact pad 33 by a ball-bond 38 and, therefore, has thecharacteristic ball or oval cross-section. In contrast to theembodiments illustrated in FIG. 2, the gold wire 27 is bonded to thealuminium wedge 41 by a stitch bond 59. The stitch bond 59 has a thinapproximately rectangular cross-section.

FIG. 4 illustrates a third embodiment of a mixed wire semiconductor leadfame package 42 according to the invention. Parts of the package 42which are essentially the same as illustrated in the embodiments of theinvention of FIGS. 2 and 3 have the same reference number and are notnecessarily described again.

In this third embodiment, the aluminium wedge 32 is positioned on thelanding pad 29 of the second lead finger 24 as illustrated in the firstembodiment of the invention. The wedge 32 is positioned so that its longlength is approximately parallel to the long length of the second leadfinger 24. In this embodiment of the invention, the gold wire 27 isbonded by a ball bond 38 to the chip contact pad 33 and to the aluminiumwedge 32 by a stitch bond 59.

FIG. 5 illustrates a schematic diagram of a detail in the first step ofthe process to produce the aluminium wedge 32 according to theinvention. A second lead finger 24 including a landing pad 29 on itsupper surface is provided. The landing pad 29 includes a first nickellayer 30 positioned on the copper leadfinger 24 and a nickel phosphorouslayer 31 positioned on the nickel layer 30.

A wedge bonding tool 43 encloses the end portion of a spool of aluminiumsource wire 44. The aluminium source wire 44 is spooled out a desiredlength and pressed using the pressing surface 45 of the wedge bondingtool 43 into the upper surface of the landing pad 29. The pressedportion 46 of the source wire 44 then undergoes a bonding treatment inwhich it is subjected to an appropriate ultrasonic energy for anappropriate time in order to bond the pressed portion 46 of the source44 wire to the landing pad 29.

FIG. 6 illustrates a schematic diagram of the second step in the processto form the aluminium wedge 32 according to the invention. After thebonding process is complete, the wedge bonding tool 43 is raised upwardsa small distance with respect to the surface of the lead finger 24 asindicated by the arrow. The wire clamp 47 of the wedge bonding tool 43then closes onto the aluminium source wire 44 and the bonding tool 43 ismoved sideways and upwards with respect to the landing pad 29, asillustrated by the arrow, in order to break the source wire 43 at aposition close to the pressed portion 46 and the landing pad 29. In thisway an aluminium wedge 32 is formed on the landing pad 29 of the secondlead finger 24.

FIG. 7 illustrates a fourth embodiment of a mixed wire semiconductorlead frame package 50 according to the invention. Parts of the package50 which are essentially the same as those of the first embodimentillustrated in FIG. 2 are indicated by the same reference number and arenot necessarily described again.

In this embodiment of the invention, the first lead fingers 23 and asecond lead fingers 24 of the copper lead frame 25 include a landing pad51 positioned towards the end of the inner portion. In contrast to theprevious embodiments of the invention, the landing pad 51 includessilver.

In this fourth embodiment of the invention, a gold bump 52 is positionedon the silver landing pad 51 of the second plurality of lead fingers 24.

The aluminium bond wires 27 are bonded with a wedge bond 37 to the chipcontact pads 33 and to the gold bump 52 positioned on the silver landingpad 51 of the second lead finger 24. The gold wires 26 are bonded to thechip contact pads by a ball bond 38 and to the silver landing pad 51positioned on the inner portion of the first lead finger 23 of the leadframe 25 by a stitch bond 59.

FIG. 8 illustrates a first multi-chip module 53 including twosemiconductor chips 54 and 55 according to the invention. Parts of themulti-chip module 53 which are similar to those of the previousembodiments are indicated by the same reference number and are notnecessarily described again.

The multi-chip module 53 includes a copper lead fame 25 including arecessed die pad 22 laterally surrounded by a plurality of first leadfingers 23 and a plurality of second lead fingers 24. A landing pad 29is positioned towards the end of the inner portion of the firstplurality 23 and second plurality 24 of lead fingers and includes a Nilayer 30 positioned on the first 23 and second 24 leadfingers and a NiPlayer 31 attached to the nickel layer The second plurality of leadfingers 24 further include an aluminium wedge 32 which is positioned onthe nickel phosphorous layer 31 of the landing pad 29.

The first 54 and the second 55 semiconductor chip are mounted laterallyadjacent to each other on the die pad 22 by die attach material 36. Eachof the semiconductor chips 54 and 55 includes a plurality of firstintegrated circuits 34, second integrated circuits 35 and chip contactpads 33 on its upper active surface. The first semiconductor chip 54 iselectrically connected by an aluminium bond wire 26 to the landing pads29 positioned on the first lead finger 23.

The first semiconductor chip 54 is also electrically connected to thesecond semiconductor chip 55 by a gold wire 56 which contacts a chipcontact pad 33 of semiconductor chip 54 with a chip contact pad 33 ofsemiconductor chip 55. The gold wire 56 is connected to the chip contactpads 33 of the semiconductor chip 55 by a ball bond 38 and to thecontact pad 33 of the semiconductor chip 54 by a stitch bond 59 on agold bump 48.

The second semiconductor chip 55 is electrically connected to the secondlead finger 24 by a gold wire 27. The gold wire 27 is connected to thechip contact pad 33 by a ball bond 38 and to the aluminium wedge 32positioned on the landing pad 29 of the second lead finger 24 by astitch bond 59. The diameter of the aluminium wires 26 is larger thanthat of the gold wires 27 which connect the second semiconductor chip tothe leadfingers 24 and the gold wires 56 which connect the first 54 andsecond 55 semiconductor chip.

The first 54 and second 55 semiconductor chips, the die pad 22, bondwires 26, 27, 56 and the inner portions, including the landing pads 29,of the first 23 and second 24 pluralities of lead fingers areencapsulated in a plastic mold material 39. The outer portions of thefirst 23 and second 24 pluralities of lead fingers extend outside of thesemiconductor package 53 and provide the external electrical connectionfor the package. The outer portions of the lead fingers 23 and 24 enablethe package 53 to be mounted on and electrically connected to anexternal substrate such as a printed circuit board (which is notillustrated in the diagram).

FIG. 9 illustrates a second multi-chip module 57 including twosemiconductor chips 54 and 55 according to the invention. Parts of thesecond multi-chip module 57 which are similar to those of the previousembodiments are indicated by the same reference number and are notnecessarily described again.

The second multi-chip module 57 further includes a chip aluminium wedge58 positioned on a chip contact pad 33 of the first semiconductor chip54. A gold wire 56 connects the first 54 and second 55 semiconductorchip of the second multi-chip module 57. The gold wire 56 is bonded tothe chip aluminium wedge 58 on the first semiconductor chip 54 by astitch bond 59 and to a chip contact pad 33 of the second semiconductorchip 55 by a ball bond 38.

The second multi-chip module 57 also includes an aluminium wedge 32positioned on the second leadfinger 24 as illustrated in the multi-chipembodiment of FIG. 8.

FIG. 10 illustrates a schematic perspective view of a section of a mixedwire semiconductor package 60 which includes grounding connections 61between the active surface of the chip 21 and the die pad 22. Thepackage encapsulation is not illustrated for clarity in this figure.

FIG. 10 illustrates a section of a semiconductor chip 21 including chipcontact pads 33 on the upper active surface. The chip 21 is mounted bydie attach material 36 in approximately the lateral centre of the diepad 22. The die pad 22 is laterally larger than the chip 21. The chip 21and die pad 22 are laterally surrounded by a plurality of first andsecond leadfingers 23, 24 of which the inner portion of three secondleadfingers 24 are illustrated in the figure.

Similarly to the embodiments of FIGS. 2 to 4, the second leadfingers 24include a landing pad 29, including a layer of Ni 30 and a layer of NiP31, and an aluminium wedge 32 positioned on the landing pad 29. Thealuminium wedges 32 are positioned approximately parallel to the lengthof the leadfingers 24. The integrated circuits 35 on the active surfaceof the chip 21 are electrically connected to the second leadfingers 24by gold bond wires 27 which extend between a chip contact pad 33 and analuminium wedge 32. The gold wires 27 are connected to the chip pad 33by a ball bond 38 and to the aluminium wedge 32 by a stitch bond 59.

In this embodiment of the invention, the die pad 22 includes groundingpads 62 positioned on the upper surface of the die pad 22 of which oneground pad 62 is illustrated in the Figure. The grounding pads 62 arelaterally positioned towards the outer edge the die pad 22 and are,therefore, positioned between the semiconductor chip 21 and the leadfingers. The grounding pad 62 also includes two electro-plated layersand includes a layer of Ni 63 positioned on the surface of the copperdie pad 22 and a layer 64 including NiP positioned on the nickel layer63.

A grounding aluminium wedge 65 is positioned on the grounding pad 62.The chip 21 is grounded to the die pad 22 by a gold grounding wire 61which extends between a contact pad 66 on the upper surface of the chip21 and the grounding aluminium wedge 65 on the grounding pad 62. Thegrounding gold wire 61 is connected to the contact pad 66 by a ball bond38 and to the grounding aluminium wedge 62 by a stitch bond 59.

1. A semiconductor package comprising: a lead frame comprising a diepad, a plurality of first leadfingers and a plurality of secondleadfingers, each including a landing pad on its inner portion; asemiconductor chip including integrated circuits and chip contact padson its upper active surface, the semiconductor chip being attached tothe die pad by its rear passive surface; a plurality of first bond wirescomprising a first electrically conductive material, each extendingbetween a chip contact pad and a landing pad of the plurality of firstleadfingers; a plurality of second bond wires comprising a secondelectrically conductive material, each extending between a chip contactpad and a second leadfinger; a plastic mould mass encapsulating thesemiconductor chip, the pluralities of first and second bond wires andinner portions of the pluralities of first leadfingers and secondleadfingers; and a plurality of first electrically conducting means, afirst electrically conducting means being attached to the landing pad ofeach of the plurality of second leadfingers, and a second bond wirebeing attached to the first electrically conducting means.
 2. Thesemiconductor package of claim 1, wherein the lead frame includes arecessed die pad.
 3. The semiconductor package of claim 1, wherein theplurality of first electrically conductive means comprises a pluralityof electrically conductive bumps or electrically conductive wedges orelectrically conductive balls.
 4. The semiconductor package of claim 1,wherein the first electrically conducting means has an approximatelyrectangular longitudinal cross-section and is positioned on the landingpad with its long side of approximately parallel to the length of thesecond leadfinger.
 5. The semiconductor package of claim 1, wherein thefirst electrically conducting means has an approximately rectangularlongitudinal cross-section and is positioned on the landing pad with itslong side of approximately orthogonal to the length of the secondleadfinger.
 6. The semiconductor package of claim 1, wherein theplurality of first bond wires is attached to the landing pads of thefirst leadfingers with a ball bond, a bump or wedge bond and theplurality of second bond wires is attached to the first electricallyconducting means on the second leadfingers with a ball-bond, a bump or astitch bond.
 7. The semiconductor package of claim 1, wherein theplurality of second bond wires and the plurality of first electricallyconducting means comprise a different material.
 8. The semiconductorpackage of claim 1, wherein the plurality of first bond wires and theplurality of electrically conducting means comprise essentially the samematerial.
 9. The semiconductor package of claim 1, wherein underwire-bonding conditions: the material of the first bond wire and thematerial of the landing pad form a eutectic; the material of the firstelectrically conducting means and the material of the landing pad form aeutectic; the material of the second bond wire and the material of thelanding pad form no eutectic; and the material of the second bond wireand the material of the first electrically conducting means form aeutectic.
 10. The semiconductor package of claim 1, wherein: the leadframe comprises copper; the landing pads comprise a layer of nickelpositioned on the surface of the first and second leadfingers and alayer of nickel phosphorous positioned on the layer of nickel; theplurality of first bond wires and the electrically conducting meanscomprise aluminium or an aluminium alloy; and the plurality of secondbond wires comprise gold or a gold alloy.
 11. The semiconductor packageof claim 1, further comprising: the lead frame comprises copper, thelanding pads comprise silver, the plurality of second bond wirescomprise aluminium or an aluminium alloy; and the plurality of firstbond wires and the electrically conducting means comprise gold or a goldalloy.
 12. The semiconductor package of claim 1, wherein thesemiconductor package includes at least one second electricallyconducting means attached to at least one chip contact pad.
 13. Thesemiconductor package of claim 1, wherein at least one secondelectrically conducting means is electrically connected to the chip padand a bond wire.
 14. The semiconductor package of claim 1, wherein atleast one second electrically conductive means comprises an electricallyconductive bump or electrically conductive wedge or electricallyconductive ball.
 15. The semiconductor package of claim 1, wherein thesecond electrically conductive means comprises essentially the samematerial as the first conductive means.
 16. The semiconductor package ofclaim 1, wherein the semiconductor package further includes a pluralityof grounding pads positioned on the die pad.
 17. The semiconductorpackage of claim 16, wherein the plurality of grounding electricallyconducting means is positioned on the grounding pads, and a groundingwire extending between a chip contact pad and the grounding electricallyconductive means.
 18. The semiconductor package of claim 17, wherein theplurality of grounding electrically conductive means comprises aplurality of electrically conductive bumps or electrically conductivewedges or electrically conductive balls.
 19. The semiconductor packageof claim 17, wherein the plurality of grounding bond wires is attachedto the grounding electrically conducting means on the die pad with aball-bond, a bump or a stitch bond.
 20. The semiconductor package ofclaim 17, wherein under wire-bonding conditions: the material of thefirst bond wire and the material of the landing pad form a eutectic, thematerial of the first electrically conducting means forming a eutecticwith the material of the landing pad, the material of the groundingelectrically conductive means and the material of the grounding padforming a eutectic; the material of the second bond wire and thematerial of the landing pad form no eutectic, and the material of thesecond bond wire and the material of the first electrically conductingmeans forming a eutectic, and the material of the grounding wire and thematerial of the grounding electrically conductive means form a eutectic.21. The semiconductor package of claim 16, wherein: the lead framecomprises copper; the grounding pads comprise a layer of nickelpositioned on the surface of the die pad and a layer of nickelphosphorous positioned on the layer of nickel; the plurality of firstbond wires, the electrically conducting means and the groundingelectrically conductive means comprise aluminium or an aluminium alloy;and the plurality of second bond wires and the plurality of groundingwires comprise gold or a gold alloy.
 22. A semiconductor packagecomprising: a lead frame comprising a die pad, a plurality of firstleadfingers and a plurality of second leadfingers, each including alanding pad on its inner portion; at least two semiconductor chipsincluding integrated circuits and chip contact pads on their upperactive surfaces attached to the die pad; a plurality of first bond wirescomprising a first electrically conductive material, each extendingbetween a chip contact pad and a landing pad of the plurality of firstleadfingers, a plurality of second bond wires comprising a secondelectrically conductive material, each extending between a chip contactpad and a second leadfinger; a plurality of third bond wires comprisinga third electrically conductive material, extending between thesemiconductor chips; a plastic mould mass encapsulating thesemiconductor chip, the pluralities of first, second and third bondwires and inner portions of the pluralities of first leadfingers andsecond leadfingers; and a plurality of first electrically conductingmeans, a first electrically conducting means being attached to thelanding pad of each of the plurality of second leadfingers, and a secondbond wire is attached to the first electrically conducting means.
 23. Asemiconductor package of claim 22, wherein the plurality third bondwires comprise essentially the same material as the plurality of secondbond wires or the plurality of first bond wires.
 24. The semiconductorpackage of claim 22, wherein the semiconductor package includes at leastone power semiconductor chip and at least one logic semiconductor chip.25. The semiconductor package of claim 24, wherein the semiconductorpackage includes at least one power chip electrically connected to thefirst leadfingers of the lead frame by a plurality of first bond wiresand at least one logic chip is electrically connected to the firstelectrical means of the second leadfingers of the lead frame by aplurality of second bond wires.
 26. The semiconductor package of claim25, wherein the first bond wires comprise aluminium or an aluminiumalloy, the second bond wires comprise gold or a gold alloy, the firstelectrical means comprises aluminium, the leadframe comprises copper andthe landing pads comprise Ni and NiP.